FIG. 4 is a schematic diagram illustrating an example of a power train of a hybrid vehicle. As shown in the figure, this vehicle comprises an engine 1 and an electric motor (or motor generator, hereinafter simply referred to as motor) 2 as drive sources 8 and a clutch (automatic clutch mechanism) 3 between the engine 1 and the motor 2, which is able to engage/disengage the transmission of driving force from the engine 1 toward the motor 2. In the output of the motor 2, a transmission 4 is connected that varies the output rotational speed from the engine 1 and/or motor 2. Namely, in this vehicle, the engine 1, clutch 3, motor 2 and transmission 4 are in this order connected in series and the driving force that is output from the transmission 4 is transmitted to driving wheels 7.
To the motor 2, a battery 6 which can be charged and discharged is connected via an inverter 5. The operational state of the motor 2 can be controlled by controlling the operation of the inverter 5.
Therefore, the vehicle can run by the assistance of driving force from the motor 2 in addition to the driving force from the engine 1 when the motor 2 is driven and the clutch 3 is engaged.
When the motor 2 functions as a generator, the battery 6 can be charged with the electricity produced by the driving force from the engine 1, and also the electric power can be regenerated by a brake, namely a regenerative brake, to the driving wheels 7. On the other hand, the driving wheels 7 can be driven only by the driving force from the motor 2 with the clutch 3 disengaged, namely, power running can be performed, by supplying power from the battery 6 to the motor 2.
The transmission 4 is a noncontinuously-variable automatic transmission, which shifts the present gear to the target one which is specified by a shift map which is not shown in the drawings. For example, it is constructed in such a way that a plurality of actuators, not shown in the drawings, are added to a parallel and biaxial gear type manual transmission. By operating the actuators, gears can be shifted.
The clutch 3 is an automatic clutch mechanism by which the clutch is automatically engaged/disengaged at the time of shifting gears and the like. The engagement/disengagement of the clutch 3 is carried out by a clutch actuator which is not shown in the drawings.
The engine 1 is a diesel engine that uses light oil as a fuel. Controlling operating time (namely, amount of fuel injection) of an injector (not shown in the drawings) of the engine 1 can control output torque of the engine 1.
The above-described vehicle shown in FIG. 4 can start off just with the motor 2.
In such a case, the vehicle starts off just by driving force from the motor 2 with the clutch 3 disengaged, and when the rotational speed of the clutch reaches a predetermined rotational speed (for example 750 rpm), an engine rotational speed synchronization control is carried out for synchronizing the engine rotational speed to the clutch rotational speed. Then, if the difference between the engine rotational speed and the target engine rotational speed, which is calculated on the basis of the engine rotational speed and the clutch rotational speed, is equal to or smaller than a predetermined synchronization-judgement threshold (for example, ±100 rpm), the clutch 3 is made engaged.
Subsequently, the vehicle runs by driving forces from both the engine 1 and motor 2. As a document showing cooperative control between an engine 1 and a motor 2 at the time of starting off of a vehicle can be cited Patent Document 1.
[Patent Document 1] Japanese Patent Laid-Open Publication No. Hei 10-68335